Admiring the rich, beautiful and monumental architecture, roads and aqueducts built by the Romans and the ingenuity of their engineers, it should not be forgotten that they were also grandmasters in a completely different field – in building fortifications. They owed their tactical advantage during the siege mainly to the talent of inventors, discipline, energy and absolute determination of soldiers.
The Romans used several methods of siege. Most often it was a blockade, but it required the use of considerable force. It consisted primarily in the construction of double fortifications around the besieged area or city. The first, called contravallatio was supposed to prevent the siege from coming out, and the second, circumvallatio was used to control the movement of enemy allies.
The most-known blockade in the history of the Roman Empire was blocking Alesia by Julius Caesar. Focusing on her example, notice how much effort and enthusiasm it cost (such as other blockades looked no less impressive and were equally effective). Impressively long fortification lines and twenty-three forts were created there. Contravallatio was sixteen kilometres in circumference, and circumvallatio as much as twenty-one. In addition, Caesar ordered a trench six meters deep near the city. One hundred and twenty meters behind it was placed circumvallatio and a ditch of four and a half meters wide and of the same depth was filled with water. The field on the other side of the excavation was filled with obstacles and traps. The soil selected from the trenches was used to build a rampart between the second fortification line and the city. A palisade was erected on the embankment and a tower was built every twenty-five meters. At the top of the embankment, there are sharpened piles protruding towards the city.
To obtain a huge amount of piles and foodstuffs, a large number of people was needed, which meant that the defence of the palisade had to be significantly reduced. This threatened to break the blockade by Vercingetorix, stationed in Alesia. Caesar found a way out of this situation. Five further ditches were dug one and a half meters deep and a fence of sharp branches was built along with them. Eight rows of pit-traps were dug in front of the fence, at the bottom of which sharpened pegs were placed, called by the legionaries as “lilies” because the shape resembled those flowers. The pits were covered with branches to mask them from the enemy. On the other side of the line, Caesar ordered to bury the trunks studded with iron skewers so that only their blades protruded from the ground. Similar safeguards were made on external lines for the army that was to come under siege. So the circumvallatio line was arranged exactly as contravallatio.
Such huge siege works were also carried out, among others near Padua during the wars with Hannibal and under Numantia and Carthage.
During the construction of the Pydna camp before the battle of Emiliusz Paulus with Perseus, legionaries broke thirteen thousand square meters of turf and moved over twenty thousand cubic meters of land, building a rampart around the camp. The construction of such blockages was usually completed within two hours. This was possible thanks to the tools that every legionary carried with him: hanks (dolabra), pickaxe-shovel (similar was worn by British soldiers during World War I) and shovel to pick turf.
The confidence of the Romans in the effectiveness of their technique of besieging areas and cities was absolute. When the commander learned that the besieged city had food supplies for ten years, he replied to the messenger that he would wait eleven years. After such a response, the inhabitants of the besieged city usually capitulated immediately.